1. Field of the Invention
The present invention relates to a display element lighting method and a display device. More particularly, the present invention relates to a display element lighting method comprising the step of lighting a display element comprising picture elements which can transmit or block light respectively by natural light together with lighting the display element by incident light from a display surface side and a back surface side of the display element, and a display device.
This application is based on Japanese Patent Application No. Hei 11-206462, the contents of which are incorporated herein by reference.
2. Description of the Related Art
A conventional display device provided with a display element having a shutter function per picture element, that is, a conventional display device provided with a display element comprising picture elements which can transmit incident light from a display surface side or block respectively is wel-known.
The following three methods have been suggested as a lighting method for the display element. The first lighting method comprises the step of lighting the display element by incident natural light from a display surface side of the display element together with lighting the display element by reflected light by a reflection surface attached to the opposite surface of the display element with respect to the display surface which transmit illumination light. The second lighting method comprises the step of lighting the display element by light from a light source arranged on the opposite surface of the display element with respect to the display surface. The third lighting method combines the first and second lighting methods by using the reflection surface attached to the opposite surface of the display element with respect to the display surface used in the first lighting method is used as a semi-transparent reflection plate.
The first lighting method is disclosed, for example, in Japanese Patent Application, First Publication No. Hei 11-86622. Moreover, the second lighting method is disclosed in Japanese Patent Application, First Publication No. Hei 07-049496, for example.
However, the first lighting method has the problem that when the display device is in dark, it is difficult to confirm the display contents at the display surface. In other words, incident light at the display surface of the display element attenuates whenever the light is reflected by the display element. Therefore, when the intensity of natural light is small, the light attenuates in the display element and the difference in the light and shade of the picture elements at the display surface is difficult to confirmed.
The second lighting method also has the problem that the light source must be lit while the display device is in use.
The intensity of the incident light is compensated in the third lighting method, and the electric power consumption is made low in the third lighting method. Therefore, it is impossible to increase the intensity of light from the light source. In addition, the display element is lit by light led from the light source into the display surface or the back surface of the display element in the third lighting method; therefore, it is also impossible to light the display element efficiently. Then, it is impossible to light the display element efficiently, and the superior visibility of the contents displayed at the display surface cannot be obtained where the display device is used in illuminated conditions.
It is therefore an object of the present invention to provide a display element lighting method in which light is used efficiently and display properties can be improved while electric power consumption needed for lighting the display element can be decreased, and a display device.
According to an aspect of the present invention, the present invention provides a display element lighting method, which has a display surface and a back surface opposite to the display surface, and comprises picture elements which can transmit or block light respectively, comprising the steps of:
lighting the display surface by a first light produced by a light source and natural light; and
lighting the back surface by a second light produced by a light source.
According to the display element lighting method, the display element is lit uniformly by the first light produced by a light source and the second light produced by a light source, from the display surface and the back surface. Thereby, the weakness of the intensity of natural light and the attenuated intensity of natural light is compensated. In addition, when the display device is used in dark conditions, it is possible to produce light having a sufficient intensity to display picture images in the display element. Furthermore, when the intensity of the light produced by the light source is adjusted in response to the intensity of natural light, not only the electric power consumption of the display device can be more decreased, but clear picture images can be produced, independently of the intensity of natural light.
Moreover, the electric power consumption can be decreased, compared with the electric power consumption of the display device in which the display element is lit by either the display surface side or the back surface side
When the first light and the second light are produced respectively by first and second light sources, it is possible to adjust respectively the intensity of light produced from the first light source and the second light source. Therefore, it is also possible to use efficiently lights, and improve the picture; properties of picture images, in addition to the decrease of the electric power consumption of the display device.
According to another aspect of the present invention, the present invention provides a display device display device comprising:
a display element having a display surface and a back surface opposite to the display surface and comprising picture elements which can transmit or block light respectively;
a first lighting device for lighting the display surface by a first light produced by a light source; and
a second lighting device for lighting the back surface by a second light produced by a light source.
According to the display device, it is possible to easily carry out the display element light method having excellent effects explained above.
In particular, when the second lighting device comprises a light leading plate having a reflection surface parallel to the display surface, and reflecting by the reflection surface or transmitting the light produced by the light source, and a second reflector which reflects the light transmitting through the light leading plate to the display surface, the light transmitting through the light leading plate can be used to light the display element. Therefore, the light produced by the light source can be used efficiently. Thereby, the electric power consumption of the display device can be decreased.